This invention relates to video-on-demand systems which send multiple streams of video data to respective viewers. In the prior art, one such video-on-demand system is described in U.S. patent application Ser. No. 09/318,987 by Urry which is entitled “Scaleable Video System Having Shared Control Circuits For Sending Multiple Video Streams To Respective Sets of Viewers” (hereafter the Urry video-on-demand system).
Included in the Urry video-on-demand system are the following components: a) a single supervisor processor, and multiple co-processors which are selectable in number and are coupled via a bus to the single supervisor processor; b) a supervisor memory which is coupled to the supervisor processor and which stores a respective portion of each of several video streams; c) a control program for each co-processor which selectively reads the stored video stream portions from the supervisor memory and sends each video stream portion that is read to a different viewer; and d) a control program for the single supervisor processor, which dynamically updates the stored portion of each video stream in the supervisor memory and which services external requests to change the respective viewers of each video stream.
One particular feature of the Urry video-on-demand system is that it is highly scaleable and economical. This feature is achieved because the number of co-processors is selectable; the number of video streams which are sent by each co-processor is selectable; and, the number of viewers per steam is selectable. By making these selections, the Urry video-on-demand system can be increased or decreased in size to meet the different requirements of many customers. Further, since the Urry video-on-demand system includes only a single supervisor processor and a single supervisor memory which operate in a shared fashion with all of the co-processors, the cost of those items is incurred only once.
However, a drawback of the Urry video-on-demand system is that to receive and show a video at the display device of any one viewer, that display device must be coupled to a transmission network thru a particular type of set-top box which has an ATM interface (asynchronous transfer mode interface) to the network. This is evident from Urry's FIG. 4 which shows that each video stream to the transmission network is sent during a series a spaced-apart time slots, with “K” bytes of video data and a network address of the viewer being sent in each time slot. A video stream with such a transmission format can only be received by a set-top box which has an ATM input interface. However, several other types of set-top boxes do exist; and a potential viewer who would like to connect to the Urry video-on-demand system might have one of those other types of set-top boxes. For example, one other type of set-top box has an “ethernet” interface to a transmission network; another type of set-top box has a “DSL” interface to a transmission network; and still another type of set-top box has a “fiber channel” interface to a transmission network.
Also, another drawback of the Urry video-on-demand system is that the transmission network, which carries the video streams from the output of the co-processors to all of the set-top boxes, must be an ATM switching network. This is because only an ATM switching network is designed to carry video streams with the above described format that is generated by Urry's FIG. 4. However, in certain locations where a potential viewer would like to connect to the Urry video-on-demand system, an ATM switching network may not be available.
Accordingly, a primary object of the present invention is to provide an improved video-on-demand system which avoids both of the above drawbacks.